S Mathias wrote: > $ true && true || echo hi Both true commands invoked. This satisfied the left hand side of the or and so echo was not invoked. > $ true && false || echo hi > hi Both true and false invoked, and then the echo. > $ false && true || echo hi > hi Only the first false invoked, and then the echo. > $ false && false || echo hi > hi Only the first false invoked, and then the echo. > $ ping -W 1 -c 4 google.com >& /dev/null | grep -q "100% packet loss" && ping -W 1 -c 4 www.yahoo.com >& /dev/null | grep -q "100% packet loss" || echo "no internet connection" > no internet connection Only the first ping|grep invoked. This returned false. The grep did not match and therefore did not return success. The grep returned a failure that it did not match. I think that is not what you expected. Since the network connection was up and online the grep 100% failed and returned false. This is exactly the same as you had tested above: > $ false && false || echo hi > hi Exactly the same and so exactly the same result. > $ ping -W 1 -c 4 google.com >& /dev/null | grep "100% packet loss" $ echo $? 1 > $ ping -W 1 -c 4 www.yahoo.com >& /dev/null | grep "100% packet loss" > $ $ echo $? 1 > ...both sides "false", because they have no output, because google.com and www.yahoo.com is reachable. > how come it writes "no internet connection"? [at the longest line] The first test is false and so the OR side with the echo is invoked. Note that the second ping|grep is not invoked. Only the first one. Being false the OR side is invoked next. > i just want a "oneliner" that checks if theres "internet connection" or no. :\ You would need to invert the grep exit code. But not using grep as you found in your later post is a better solution. > where did I screw up? 8) You used ">& /dev/null" to redirect both stdout and stderr to /dev/null. This means that there isn't any input to grep and therefore grep can never succeed with a match. Side Note: You are using ">& word" which is not typical. The manual states that using "&> word" is preferred over ">& word". I believe this to reduce confusion over the "2>&1" syntax. When in doubt follow the documentation. Personally I never use that bash specific syntax and stick with the standard ">/dev/null 2>&1" syntax. And if the standard syntax had been used in this case I think it would have made the issue obvious at a glance. Bob
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